plastic mould, injection mould

What is relate to the plastic material shrinkage?

Plastic material shrinkage not only relate to the plastic material, but also relate to the other external factors. So the factory provide a range of plastic material shrinkage instead of a fixed value for manufacturer. The following detailed analysis will tell you three factors that affect the injection material shrinkage size.

     The first: the injection mold structure. Gate form also will affect the shrinkage. With small gate, because the gate will curing before the overpackaging finished and make the plastic pieces shrinkage increases. The cooling waterway structure of injection mold is one of the keys for mold design. Cooling waterway design is not proper, the plastic parts will have shrinkage difference because of temperature disequilibrium in everywhere. It will make plastic parts dimension out-of-tolerance or deformation. In the thin-wall part, the effect of mold temperature distribution on the shrinkage is more obvious.

    The second: forming conditions: material barrel temperature. Material barrel temperature (plastic temperature)is high, pressure transmit better and make the contraction force decrease. But with small gate, because gate curing early and make the shrinkage large. For thick wall plastic parts, even if the material barrel temperature is high, the shrinkage is still large.

    The third: the shape of plastic parts. For wall thickness of forming parts, generally because the cooling time of thick wall is long, so the shrinkage is bigger. In general, for the plastic parts, a direction size is very different from the other direction size, the shrinkage difference is also bigger. See from the flow distance of molten material , the pressure loss of part which is away from the gate is big, thus its shrinkage is larger than the near gate position.

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